The present invention relates to a puffer type gas-insulated circuit breaker that extinguishes an arc by blasting an insulating gas on the arc, and particularly to a gas-insulated circuit breaker having the improved structure of an insulating nozzle that blasts the insulating gas.
The gas-insulated circuit breaker is a device in which a pair of contacts is disposed inside a sealed container filled with insulating gas, and is often used as an on-off switch for electric current in an electric power transmission and distribution system. Hereinafter, an example of a conventional puffer type gas-insulated circuit breaker will be described in detail with reference to FIGS. 6 and 7.
FIG. 6 is a cross-sectional view of the puffer type gas-insulated circuit breaker. FIG. 7 is an enlarged cross-sectional view of an area near an arc 8. Both diagrams show a state during an opening operation. Each of components of the gas-insulated circuit breaker illustrated in the diagrams is basically in the shape of a coaxial cylinder. FIG. 7 illustrates only the upper half of the gas-insulated circuit breaker above a central axis.
As shown in FIG. 6, the puffer type gas-insulated circuit breaker is provided with a sealed container 1 that is made of grounded metal, insulator, or the like. An arc-extinguishing gas 2 of an insulating gas such as SF6 gas (sulfur hexafluoride gas) fills up the sealed container 1. SF6 gas has an excellent arc-extinguishing and electric insulating capability. The electric current on-off device filled with the gas is the mainstream of the high voltage electric transmission systems.
Inside the sealed container 1, as the pair of contacts, a fixed contact section 21 and a movable contact section 22 are so disposed as to face each other. The fixed contact section 21 and the movable contact section 22 can be connected and separated as desired. The fixed contact section 21 is fixed inside the sealed container 1, while the movable contact section 22 is connected to a driving mechanism through an operating rod (not shown) and can be moved in the left and right direction in FIG. 6 as desired. During operation, a high voltage is applied to the contact sections 21 and 22, and insulation is maintained by support insulating bodies 12 (only one of which is illustrated on the part of the fixed contact section 21 in FIG. 6). The contact sections 21 and 22 are mechanically supported by the support insulating bodies 12 inside the sealed container 1.
A fixed arcing contact 7a and a movable arcing contact 7b are provided on the fixed contact section 21 and the movable contact section 22, respectively. The arcing contacts 7a and 7b are in contact and conduction state during normal operation. During the opening operation, the arcing contacts 7a and 7b are separated from each other as the movable arcing contact 7b moves along with the movable contact section 22. When the arcing contacts 7a and 7b are separated from each other, the arc 8 occurs in a space between the arcing contacts 7a and 7b. 
The following describes the configuration of the fixed contact section 21. On the opposite side (the left side in FIG. 6) of the fixed contact section 21 from the side facing the movable contact section 22, an exhaust pipe 9 made of metal is attached. A fixed-side hot gas flow 10a that flows from the space where the arc 8 occurs toward the fixed contact section 21 passes through the exhaust pipe 9. The upstream area of the fixed-side hot gas flow 10a that passes through the exhaust pipe 9 is around the arc 8, and the downstream area is around the internal space of the sealed container 1.
The following describes the configuration of the movable contact section 22. In the movable contact section 22, a hollow rod 11 is provided. The hollow rod 11 is connected to the movable arcing contact 7b. The hollow rod 11 is extends toward the opposite side (the right side in FIG. 6) of the movable contact section 22 from the side facing the fixed contact section 21. A movable-side hot gas flow 10b that flows from the space where the arc 8 occurs toward the movable contact section 22 passes through the hollow rod 11. That is, like the fixed-side hot gas flow 10a, the upstream area of the movable-side hot gas flow 10b that passes through the hollow rod 11 is around the space where the arc 8 occurs, and the downstream area is around the internal space of the sealed container 1.
Moreover, on the movable contact section 22, a gas flow generation means is provided as a distinctive component of the puffer type gas-insulated circuit breaker. The gas flow generation means is a means to generate a gas flow 10c from a puffer chamber 5. The gas flow 10c is blasted on the arc 8. After being blasted on the arc 8, the gas flow 10c is divided into the gas flows 10a and 10b described above.
The major components of the gas flow generation means are a piston 3 fixed on the sealed container 1 and a cylinder 4 that houses the piston 3. The piston 3 can slide in the cylinder 4 as desired. The internal space of the cylinder 4 serves as the puffer chamber 5. An insulating nozzle 6 is disposed on the front end section (the left side in FIG. 6) of the cylinder 4. The insulating nozzle 6 communicates with the puffer chamber 5. The cylinder 4 is attached to the movable contact section 22. The insulating nozzle 6 is made of a heat resistance insulating material such as polytetrafluoroethylene, and emits an arc-extinguishing gas 2 stored in the puffer chamber 5 as the above-described gas flow 10c, with the narrowest portion of a gas passage 6a serving as a throat section 6b. 
The following describes the correlation in diameter between the insulating nozzle 6 and the arcing contacts 7a and 7b. As described above, FIGS. 6 and 7 illustrate a state during the opening operation. The arcing contacts 7a and 7b are therefore separate from each other. However, when the gas-insulated circuit breaker is turned on, i.e. the contacts are in “closed” state as a switch, both arcing contacts 7a and 7b need to be in contact and conduction state.
Accordingly, as shown in FIG. 7, the correlation between the outer diameter φF1 of the fixed arcing contact 7a and the inner diameter φM1 of the movable arcing contact 7b is as follows:
φF1>φM1. The movable arcing contact 7b that moves is always in contact with the fixed arcing contact 7a. 
Moreover, the insulating nozzle 6 blasts the gas flow 10c toward the arc 8 generated between the arcing contacts 7a and 7b. The insulating nozzle 6 is so formed to encircle the arcing contacts 7a and 7b. Therefore, it is clear that the inner diameter φN1 of the throat section 6b need to be set larger than the outer diameter φF1 of the fixed arcing contact 7a. That is, the correlation in diameters between the insulating nozzle 6 and the arcing contacts 7a and 7b is as follows: The diameter of the insulating nozzle 6, the fixed arcing contact 7a, and the movable arcing contact 7b becomes smaller in that order, i.e. φN1>φF1>φM1.
The following describes an arc interruption process of the gas-insulated circuit breaker having the above configuration with reference to FIG. 7. During the opening process of the gas-insulated circuit breaker, the driving mechanism (not shown) operates to move the movable contact section 22 in the right direction in FIG. 7, thereby separating the movable contact section 22 from the fixed contact section 21. In response, the cylinder 4 fixed on the movable contact section 22 also moves in the right direction in FIG. 7.
At this time, the piston 3 in the cylinder 4 moves relatively in the left direction in FIG. 7 to compress the puffer chamber 5, thereby increasing the pressure of the arc-extinguishing gas 2 inside the puffer chamber 5. As a result, the arc-extinguishing gas 2 inside the puffer chamber 5 flows toward the insulating nozzle 6 as a high-pressure gas flow 10c. Therefore, the insulating nozzle 6 blasts the strong gas flow 10c on the arc 8 generated between the arcing contacts 7a and 7b. Thanks to the gas flow 10c, the conductive arc 8 disappears, ensuring the interruption of electric current.
The gas flow 10c that is blasted on the high-temperature arc 8 is heated to a high temperature, and is divided into the fixed-side hot gas flow 10a and the movable-side hot gas flow 10b. The fixed-side hot gas flow 10a and the movable-side hot gas flow 10b then flow away from the area where the arc 8 occurs between the arcing contacts 7a and 7b, pass through the exhaust pipe 9 and the hollow rod 11, respectively, and are finally released in the sealed container 1.
The following describes a physical mechanism of interrupting the arc 8 by blasting the gas flow 10c during the above-described arc interruption process. Here, FIG. 8 is used along with the above-described FIG. 7. A diagram on the upper side of FIG. 8 is a cross-sectional view of the throat section 6b of the insulating nozzle 6 along the radial direction, and a diagram on the lower side of FIG. 8 illustrates the temperature distribution inside the throat section 6b. 
The gas flow 10c that enters the insulating nozzle 6 from the high-pressure puffer chamber 5 flows at the fastest speed through the throat section 6b that is the narrowest point of the gas passage 6a of the insulating nozzle 6. Since electric current flows through the arc 8, the temperature of the gas flow 10c is high due to Joule heating.
That is, when the gas flow 10c is being blasted on the arc 8, the gas flow 10c that is flowing around the high-temperature arc 8 at high speed is lower in temperature than the arc 8. Therefore, when the arc 8 is being interrupted, the temperature distribution inside the throat section 6a of the insulating nozzle 6 is high around the central portion, i.e., the arc 8, as shown in the diagram on the lower side of FIG. 8. The temperature distribution becomes lower toward the wall surface of the throat section 6b, i.e., the peripheral portion. The temperature gradient is extremely steep.
Therefore, in the lower-temperature gas flow 10c that flows outside the arc 8 at high speed, a heat flow 41 (illustrated in FIG. 8) occurs from the central portion toward the peripheral portion, depriving the arc 8 of heat. Therefore, the arc 8 is cooled down. The electric conductivity of the arc 8 monotonically decreases as the temperature decreases. Therefore, the electric conductivity of the arc 8 significantly decreases as the arc 8 is cooled down. As a result, the arc 8 is cooled down until the arc 8 becomes an insulator, ensuring the interruption of electric current.
Moreover, the fact that the temperature of the arc 8 reaches several tens of thousands K around an over-current peak also contributes to the interruption of electric current. That is, during the process of interrupting the arc 8, the insulating nozzle 6 is being exposed to the extremely high temperature of the arc 8. Therefore, the component of the insulating nozzle 6, which is an insulating material like polytetrafluoroethylene, melts and is gasified. It is known that as a result, an ablation gas 31 emerges from the inner wall of the throat section 6b as shown in FIG. 7.
Accordingly, the gas flow 10c that is blasted from the insulating nozzle 6 to the arc 8 is not made of only the arc-extinguishing gas 2 but is a mixed gas of the arc-extinguishing gas 2 and the ablation gas 31. When the component of the solid insulating nozzle 6 is gasified, the volume increases significantly, resulting in a large value that represents the volume of the ablation gas 31.
That is, the pressure of the puffer chamber 5 further increases as the ablation gas 31 is generated from the insulating nozzle 6, promoting an increase in the pressure of the gas flow 10c and having a preferable effect to interrupt the arc. The above has described the typical configuration of the puffer type gas-insulated circuit breaker and the principle of arc interruption.
A puffer type gas-insulated circuit breaker, like the one described above, can achieve a high arc-extinguishing capability by blasting the arc-extinguishing gas 2 stored in the puffer chamber 5 on the arc 8 generated at the time of electric current interruption. Therefore, such a puffer type gas-insulated circuit breaker is widely used as a protective on-off switch in a high voltage electric transmission system for 72 kV or more and has been improved in various ways.
For example, the conventional arts disclosed in Japanese Patent Publication No. 7-97466 (Patent Document 1), Japanese Patent Publication No. 7-109744 (Patent Document 2) and Japanese Patent Application Publication No. 2001-283693 (Patent Document 3), the entire contents of which are incorporated herein by reference, are well known. Here, although the mechanisms disclosed in Patent Documents 1 to 3 are not described in detail with reference to drawings, the outlines of the mechanisms will be described with reference to the above-described FIG. 7. According to Patent Document 1, holes are formed around the hollow rod 11 near the movable contact section 22. The movable-side hot gas flow 10b is heated to high temperatures as the arc 8 occurs. Therefore, at the initial stage of the operation in which the arc 8 is interrupted, the puffer chamber 5 actively takes in the high-temperature movable-side hot gas flow 10b via the holes (not shown in FIG. 7) of the hollow rod 11, thereby contributing to the increase in the pressure of the puffer chamber 5.
Moreover, in the gas-insulated circuit breaker disclosed in Patent Document 2, the puffer chamber 5 is divided into two along the axial direction, thereby limiting the capacity of the puffer chamber 5 near the arc 8, thereby increasing the blasting pressure for the arc 8 especially at the time of interrupting large electric current. Moreover, a check valve (not shown in FIG. 7) is provided at the division section of the puffer chamber 5, avoiding applying a high pressure directly on the piston 3. Therefore, an increase in driving force of the movable contact section 22 is prevented.
Furthermore, the gas-insulated circuit breaker disclosed in Patent Document 3 is characterized by a magnetic field generation means (not shown in FIG. 7) that is provided in addition to a gas flow generation means for generating a flow component in the radial direction of the arc 8: The magnetic field generation means generates magnetic pressure in the radial direction of the arc 8. Such a gas-insulated circuit breaker can extinguish the arc while squeezing the arc 8 in the radial direction in a portion of the area where the arc 8 occurs.
That is, according to the technique of Patent Document 3, a combined effect of two separate effects, which do not interfere with each other, can be obtained: the fluid effect of gas flows and the electromagnetic effect of magnetic fields. Therefore, it is possible to decrease the arc time constant by efficiently squeezing the arc diameter, thereby swiftly extinguishing the arc 8.
According to the conventional arts like those disclosed in Patent Documents 1 to 3, it is possible to actively take advantage of the heat energy of the arc 8 or the electromagnetic energy of magnetic fields as the energy to increase the pressure of the puffer chamber 5 as well as the mechanical compressive effect of the piston 3, increasing the blasting pressure of the arc-extinguishing gas 2 and leading to an improvement in opening performance.
Moreover, the conventional arts like those disclosed in Patent Documents 1 to 3 are less dependent on the mechanical compression by the piston 3 because of the use of the other energy sources, compared with an ordinary gas-insulated circuit breaker that can achieve an increase in the pressure of the same puffer chamber 5. Therefore, even the small piston 3 can increase the pressure enough to interrupt electric current.
Therefore, the gas-insulated circuit breaker can be downsized, and the amount of gas that fills the sealed container 1 can be reduced. Moreover, thanks to the introduction of the small piston 3, less energy is required to drive the movable contact section 22. Thus, the driving mechanism is downsized, costs are reduced, and mechanical reliability and economic efficiency are increased.
In the gas-insulated circuit breaker of a type that actively uses the heat energy of the arc 8, if the amount of the arc-extinguishing gas 2 in the puffer chamber 5 is not enough, the pressure inside the puffer chamber 5 does not increase easily or falls immediately after an increase in the pressure inside the puffer chamber 5.
In such cases, even if the puffer chamber 5 takes in the heat energy of the arc 8, the thermal compression effect of the arc 8 cannot be tapped effectively. Moreover, if the thermal compression effect of the arc 8 is used less frequently, then it becomes difficult to reduce the mechanical compression effect relatively. As a result, it becomes difficult to achieve such effects, like a reduction in driving force or preventing an increase in the amount of contained gas, which lead to the downsizing of the device.
Accordingly, in the gas-insulated circuit breaker of a type that takes the heat energy of the arc 8 in the puffer chamber 5, it is important to make the passage cross-section area S1 (shown in FIG. 7) of the gas passage 6a of the throat section 6b of the insulating nozzle 6 small in size and to limit the amount of the gas flow blasted from the insulating nozzle 6, in order to reduce the amount of the gas flow exhausted from the puffer chamber 5.
However, if the passage cross-section area S1 of the gas passage 6a is simply made small, new problems arise. That is, making the passage cross-section area S1 of the gas passage 6a small means making the inner diameter φN1 of the throat section 6b of the insulating nozzle 6 small. As described above, as for the diameters of the insulating nozzle 6 and the arcing contacts 7a and 7b, the correlation φN1>φF1>φM1 remains unchanged given the certainty of the contact and conduction state between the contacts 7a and 7b. 
Therefore, when the inner diameter φN1 of the throat section 6b of the insulating nozzle 6 is narrowed, the outer diameter φF1 of the fixed arcing contact 7a and the inner diameter φM1 of the movable arcing contact 7b need to be narrowed more. That is, the tiny components constitute the arcing contacts 7a and 7b. As a result, the arcing contacts 7a and 7b can be easily damaged at the time of electric current interruption, and the durability of the arcing contacts 7a and 7b, as members, decreases (More specifically, the number of times electric current is interrupted before the replacement of the arcing contacts 7a and 7b drops).
Moreover, when the contacts of the gas-insulated circuit breaker are separated, a high voltage is applied to between the arcing contacts 7a and 7b. At this time, the electric current insulating state needs to be maintained. If the diameters of the arcing contacts 7a and 7b are small, the electric field intensifies at the tips of the arcing contacts 7a and 7b. Therefore, in order to ensure the opening operation for the high electric field, it is necessary to increase the separation distance between the arcing contacts 7a and 7b and the speed in separating the arcing contacts 7a and 7b. 
That is, even if the heat energy of the arc 8 is used to increase the pressure of the puffer chamber 5 to reduce the driving energy, the effectiveness of driving energy reduction decreases accordingly as the separation distance and the separating speed increase due to the reduction in diameter of the arcing contacts 7a and 7b, making it difficult to downsize the device.
As a conventional art to solve the above problems, a gas-insulated circuit breaker is for example proposed in Japanese Patent Application Publication No. 2004-39312 (Patent Document 4), the entire content of which is incorporated herein by reference. According to the technique, in order to change the size of the gas passage cross-section area inside the insulating nozzle 6, a gas passage adjustment mechanism (not shown) is provided that has an iris diaphragm structure used in a camera or the like. Thanks to the operation of the gas passage adjustment mechanism, the passage cross-section area S1 of the gas passage 6a of the insulating nozzle 6 decreases in size in accordance with the operation of separating the contacts of the contact section.
That is, in the gas-insulated circuit breaker disclosed in Patent Document 4, the passage cross-section area S1 of the gas passage 6a is reduced in size by the gas passage adjustment mechanism, thereby reducing the amount of the gas flow 10c flowing from the insulating nozzle 6 at the time of separating the contacts of the contact section. Therefore, a sufficient amount of the arc-extinguishing gas 2 remains in the puffer chamber 5 when the puffer chamber 5 takes in the heat energy of the arc 8, thereby making it possible to increase the contribution of the heat energy of the arc 8 to the increase in the pressure of the puffer chamber 5.
Moreover, the passage cross-section area S1 of the gas passage 6a of the insulating nozzle 6 is controlled by squeezing the gas passage adjustment mechanism. Therefore, the inner diameter φN1 of the throat section 6b of the insulating nozzle 6 need not be narrowed. Moreover, the arcing contacts 7a and 7b also need not be narrowed in diameters. Therefore, it is possible to avoid such problems like a decrease in durability of the arcing contacts 7a and 7b and a rise in electric field at the tips of the arcing contacts 7a and 7b, which are associated with the smaller diameter. Accordingly, it is possible to suppress the electric field at the tips of the arcing contacts 7a and 7b, and it is not necessary to increase the separation distance of the contacts 7a and 7b and the separating speed. As a result, driving energy can be reduced, and the device can be downsized.
As described above, in the gas-insulated circuit breaker disclosed in Patent Document 4, the gas passage adjustment mechanism is provided to suppress the amount of the gas flow exhausted from the puffer chamber 5 via the insulating nozzle 6, leading to an increase in the pressure of the puffer chamber 5 with the help of the heat energy of the arc 8 and resulting in a further improve in opening performance.
However, the following problems with the conventional puffer type gas-insulated circuit breakers have been pointed out. That is, since the puffer type gas-insulated circuit breaker is designed to blast the arc-extinguishing gas 2 on the arc 8, the opening performance is largely determined by the cooling capability of the arc-extinguishing gas 2. As a conventional arc-extinguishing gas 2, SF6 gas having a high cooling capability is widely used. However, these days, the use of SF6 gas entails the following problems.
SF6 gas is recognized as a man-made gas that is a major contributor to global warming. In terms of environmental protection, it is desirable that the amount of SF6 gas to be used should be reduced. Accordingly, a natural gas that has less impact on the environment, such as N2 gas or CO2 gas, is under consideration as a substitute gas for SF6 gas.
However, when the substitute gas is used, the substitute gas has a lower cooling capability compared with SF6 gas because the substitute gas and SF6 gas are different in physicochemical properties. Therefore, the problem is that the cooling effect of the arc 8 decreases. Accordingly, when N2 or CO2 gas is used, a structure is urgently required that can increase the cooling effect of the arc 8 without depending on the cooling capability of the arc-extinguishing gas 2.
The gas-insulated circuit breaker disclosed in Patent Document 4 is of a type that actively makes use of the heat energy of the arc to increase the pressure of the puffer chamber and is provided with the gas passage adjustment mechanism. Therefore, the amount of the gas flow flowing from the insulating nozzle can be efficiently suppressed. Moreover, it is possible to increase the contribution of the arc heat to the increase in the pressure of the puffer chamber. However, the gas passage adjustment mechanism employs the iris diaphragm structure used in a camera or the like. Accordingly, the number of components of the gas passage adjustment mechanism increases. Moreover, since the components of the gas passage adjustment mechanism work in conjunction with each other, it takes time to adjust or assemble the gas passage adjustment mechanism to ensure the smooth operation of the components. The problem is, therefore, that as for the members that work to suppress the amount of the gas flow from the insulating nozzle, production costs are high.